Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


small metallic bridging

Glen brian

#8300

small metallic bridging | 6 December, 1999

Recently, my plant met the problem of bridging, a metallic link, lying on the solder mask and joining nearby joints. It is very diffcult to observe by our inspector and may be only discovered with ICT testing. This defect ocurrs randomly around the board and only at some boards. I would like to know the root cause of it and how to solve this problem

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#8301

Re: small metallic bridging | 6 December, 1999

Glen: So that's this metal? Is it in the area of PTH or SMT solder connections? Etc, Etc. Assuming its near connections where pasted is reflowed ...

Reflow defects, bridging: misplaced components, high placement force mushrooms paste, too much paste, paste slump, misplaced paste.

Check the archives.

Good luck

Dave F

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#8302

Re: small metallic bridging | 6 December, 1999

Hi Glen, is it a wavesoldering or reflow problem ? Check the difference between the boards that show this symptom and those that doesn�t. Are there differences in the material, the handling, the processes, pitches etc. Looking at that should help you a lot.

Good luck Wolfgang

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Glen brain

#8303

Re: small metallic bridging | 9 December, 1999

Hi,

It is wavesoldering defect, in single- sided copper board, using alcohol-based rosin flux. It is not a bridging between the protruding leads but a metallic (I think, it is solder) link, varies in dia./thickness, connected the basement of solder joint.

It occurs randomly on the board without any fix pattern. I hope my clarification can help you to understand my problem

Thanks

Glen

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#8304

Re: small metallic bridging | 10 December, 1999

Hi Glen,

looks like flux or solder mask problem. In your first mail you said that only some boards show these symptoms and others not. First I would check on the differences between those Boards, manufactorer, solder resist, contamination. If that doesn�t help or brings no results, means your Boards are allright, check your flux system for uniform and regular flux film seen best after preheat. If you use a foamfluxer sometimes depending on the cleanliness of the ceramic tube you get to big bubbles and some parts/dots of the PCB are not fluxed correctly. Check your preheat, flux should be dried out after preheat. If you use fixtures make sure they are cooled down before you send them back in. Hot fixtures make the foam collapse. To me it looks like a flux problem.

Good luck

Wolfgang

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#8305

Re: small metallic bridging | 10 December, 1999

Glen: Thanks for the clarification.

I agree with Wolfgang that fluxer setup could be the source of the problem. Bottom-side wave solder shorting has a fairly wide range of potental causes. For instance slow conveyor speed can produce the same conditions as poor fluxing because too much flux is washed from the board.

Let me take my guess to the opposite end of the machine. I'm going to swing for the fence with dross contaminated solder, caused by recirculating the dross through the pot to the assembly. Fixing this requires pulling the pump and nozzles and cleaning the pot.

Good luck

Dave F

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Kris W

#8306

Re: small metallic bridging | 14 December, 1999

Glen,

Although the previous answers probably fit the problem you are having, we recently found that during pin insertion on an Autosplice machine, the gold was flaking from the pins and lodging between the legs of surface mount components. It would actually reflow into the solder joints during second side reflow. Just another possiblity - however remote!

Kris

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